In regards to music, I personally (in opinion ONLY, I am not saying this is the right way to go) categorize music in one of four groups: Fun, Artistic, Not For Me, and Shit. I am not going to name bands or artists that I would put into the "Shit" category, as I do not wish to be the bringer of the inevitable flame war where people begin claiming others have no taste in music, and that they need to grow up or are idiotic for liking a certain type of music. Finally, another disclaimer is that I do indeed listen to most sorts of music, primarily metal, rock, and foreign music, though I do listen to pop, some hip-hop, techno, trance, and a little bit of country once in a while in small doses. That said, here are my thoughts:
"Fun" music: I see this as catchy music that can be listened to just to relax or when you need to destress and unwind and just hear something in the background. I tend to listen to this category somewhat often, but I do not see depth outside of this category being used as anything other than throwaway entertainment. It is an art to be able to make music that fits here, but I do not consider this SIGNIFICANT art. Examples of this: Black Eyed Peas, P!nk, half of Lady Gaga's work, old Disturbed, Psycho le Cemu, Rob Zombie, Lordi, Static-X, most video game soundtracks.
"Artistic" music: I view this as music that has had obvious effort expended by the artist in making the music, usually with personal experience and values inserted into the music. I would also call this "contemporary" music, in that it often involves artists turning a new leaf and trying their hand at something they have never done before. However, there are many bands that put out music I consider artistic that retain a similar sound throughout their career. If I can tell that thought went into the lyrics and pacing/overall layout of the song, or that the band/artist put a lot of blood, sweat, and tears into making the music, I consider it significant art. I listen to this category quite a bit, and when I do, I usually focus solely on the music and aim to appreciate it. Bands under this category are also usually made up of people who I respect, with visions and attitudes that they express in music and interviews. Of the bands listed, I find almost all of the artists/bands interesting as people and respect their work, and as such, they are in a way idols to me. Examples: Dir en grey (ESPECIALLY the entire Uroboros album), Mastodon, Russian Circles, the other half of Lady Gaga's work, old In Flames (up to and including Clayman)
"Not For Me" music: Music that I can appreciate as artistic, but I personally just do not understand it. Examples: Isis, can't think of any others at the moment.
"Shit" Music: LOL RAP LOL. But seriously, shit can come from any genre, and no, I do not have an actual bias against rap itself. This is music that I cannot see having any value, artistic or not, and will lead me to seriously question the intelligence of its fans. I'm not one to totally shut myself off to someone based on something like musical taste, but liking artists I would put under this category will earn you at least a raised eyebrow from me.
That being said, I consider almost all music art, and feel that music is a very personal thing. To each his own, and if you appreciate the music on a level beyond "I like to have this in the background while I study/drive/whatever", then to you it should be considered significant art.
As an ending note, I am a 20 year old straight male college student, and am a huge supporter of Lady Gaga. If you feel the need to bash her, that is your right and I will not stop you or say anything more about it. However, I suggest we all keep an open mind and not just jump on someone as an idiot or as having no taste for a few musical preferences. Music can mean something different to each person, and I respect her as both a person and an artist. Remember, the common stereotype isn't always right. People are people, and much more than the type of sound they like hearing. Cheers, and I hope this remains a well-reasoned discussion instead of turning into a flame war.